Producing nickel alloy articles



Patented May 23, 1939 UNITED STATES PRODUCING NICKEL ALLOY ARTICLES LeoSchlecht, Ludwigshaien-on-the-Rhine, and Walter Schubardt, Mannheim,Germany, assignors to I. G. Farbenindustrie Aktiengescllschaft,Frankfort-on-thc-Main, Germany No Drawing. Original application October25,

1934, Serial No. 749,922.

Divided and this anplication May 21, 1936, Serial No. 81,022. In GermanyMarch 26, 1928 Claims.

, the said articles being difierent from, and superior to, any metallicarticles of substantially the same composition which have been knownprior to the present invention. Throughout this application and theappended claims the termarticles" is used in a broad sense including notonly worked pieces of nickel alloys, but also coherent lumps of more orless irregular shape which may serve for making worked pieces therefrom,but is not meant to include nickel alloys in the form of coarse or finepowder.

More particularly, this invention relates to articles consisting ofnickel alloys, especially those with iron, chromium, manganese, copperor severalof these elements.

In order that our invention and the advantages inherent therewith may befully understood it may be convenient first to give a brief summary ofthe prior art and the disadvantages .which are experienced in the knownprocesses.

Prior to the present invention, nickel articles have been preparedmainly from the so-called cube-nickel" or from the small nickel ballsprepared by the Mond process.

Cube-nickel is preparedby intimately mixing nickel oxide and carbon,making the mass into cubes and heating to a reduction temperature.

The resulting nickel contains copper and at least from 0.2 to 0.3 percent of carbon and often further impurities. In order to make nickelarticles from this material, it must be subjected to a nickel used asinitial material which, moreover,

is impure itself.

The small nickel balls from the Mond process. 7

i. e. a process in which nickel carbonyl is therv mally decomposed onsmall nickel particles kept in continuous movement, also require amelting operation for being worked into nickel articles, in whichmelting process the same disadvantages are experienced 'as'in the caseof cubenickel.

Metallic nickel may also be produced by elec trolyzing solutions ofnickel salts. The resulting nickel can as a rule be worked into nickelarticles only by a melting operation which is attended not only with thedisadvantages discussed above, but with the further drawback that thenickel contains substantial amounts of hydrogen so that large amounts ofgas are evolved during the melting operation giving rise to an articlewith more or less great cavities and having a low mechanical strength.

Nickel is also known commercially in a pulverulent form. Such nickel maybe obtained by the reduction of finely divided nickel oxide by means ofreducing gases such as hydrogen.

When such pulverulent nickel is melted, the same disadvantages areexperienced as in the melting processes referred to above.

Attempts have also been made to produce metallic articles from more orless finely subdivided metals by a method which avoids the meltingoperation'and the contamination of the material involved therein andconsists in subjecting the While such a sintering operation has beencarried through successfully for example with iron, it has been acomplete failure in the case of nickel. Even when attempting to producenickel articles by consolidating by sintering .the pulverulent nickel ofhighest purity which is. ob-

tained by the reduction of nickel oxide, products are obtained which aresintered only incompletely and thus have a low mechanical strength whichis insuflicient for practical purposes. ample, when such nickel articlesare subjected to a rolling or forging treatment, they are always liableto become destroyed by cracks or fissures.

All past experiences have thus led to the conclusion that it isabsolutely necessary, in order to obtain nickel articles of sufficientlyhigh strength, to have small amounts of manganese or magnesium presenttherein. Even the socalled pure nickel articles of commerce,.such as arewidely used in the chemical industry as well as for household and otherpurposes, never consist of pure nickel, but always contain only up to 98or 99 per cent of nickel and in addition thereto manganese, and oftenalso magnesium, copper and cobalt.

These additions as well as carbon and sulphur tend to reduce theresistance of the nickel articles to corrosion.

The aforesaid impurities of commercial nickel articles not only lead tothe disadvantages referred to in the foregoing, but they involve the'oxide.

further drawback that nickel could hitherto be welded only withdifliculty, if at all, and the welding seams were often very brittle dueto occluded gases and in any case of inferior strength.

Similar considerations apply, of course, to alloys of nickel, moreparticularly with iron, chromium, larger amounts of manganese, copper,or several of these metals. All alloys of this kind hitherto availablein commerce have been obtained by way of a melting operation.

In the course of the last years, finely subdivided nickel has becomecommercially available which is produced by thermally decomposing nickelcarbonyl in the free space of a vessel heated to decompositiontemperature, for example in accordance with the U. S. Patent No.1,759,661. This nickel is of about the same degree of purity as thenickel obtained by the reduction of nickel It has therefore hithertobeen assumed that the nickel obtained from nickel carbonyl would havethe same properties as the latter kind of nickel, and it has beenconverted into nickel articles or nickel alloy articles exclusively bythe method of melting.

It was therefore highly surprising when we discovered that the nickelobtained from nickel carbonyl constitutes an excellent material for theproduction of metal articles by the sintering method, provided certainprecautions are taken which we shall explain below. It is this discoverythat, the invention disclosed in our application for patent Ser. No.749,922, filed October 25, 1934, and the invention described in thepresent specification whichis a division froni'the said application forpatent are based upon.

Nickel obtained by the thermal decomposition of nickel carboyl in thefree space of a heated vessel is characterized by being a fine powder.Analysis shows that it is free from manganese, magnesium, copper,silicon and phosphorus, and that it contains less than 0.002 per cent ofsulphur. Its carbon content is usually very low, for example up to 0.03per cent, though in some cases it may amount to 0.2 per cent or evenmore. It is this material that we make use of according to our presentinvention.

Pure nickel articles are obtained by our process from this materialwhich are characterized by the following properties: They contain atleast 99.9 per cent of nickel, are free from manganese, magnesium,copper, silicon and phosphorous and do not contain more than 0.03- percent of carbon and not more than 0.002 per cent of sulphur. Asa resultofthis extreme purity, our new nickel articles can be welded without anydifliculty,

and the welding seams have the same mechanical strength as theyremaining portions of the material. Our new nickel articles are furthercharacterized by a particularly high softness or ductility, whereby theyare easily worked in the cold as well as in the warm. They areparticularly adapted for being stamped or rolled without suffering fromfissures or cracks. In view of their quite peculiar and outstandingproperties, our new nickel articles are eminently suitable, for examplefor use as anodes for electroplating with nickel, since the solutionsremain sufliciently pure for a long time and the nickel precipitateproduced on the cathode is more uniform, and for the production ofnickel wire, forthe construction of thermionic valves and .the like,since no occluded gases or other noxious substances are given off invacuo.

The same kind of nickel is made use of for the production of alloys inaccordance with the present invention. These alloys contain, in additionto nickel, one or more of the metals iron, chromiu copper and manganese.They are further characterized by a sulphur content of less than 0.002per cent and a carbon content of less than 0.3 per cent, preferablybelow 0.2 per cent. They possess a high mechanical strength so that theycan be rolled in the cold and, especially in the case of alloyscontaining iron, excellent magnetic and electric properties.

In the case of nickel-iron alloys the iron content usually rangesbetween 40 and 75 per cent; the content in manganese in the case ofnickelmanganese alloys usually ranges between 0.1 and 2 or 3 per cent,whilein the case of nickel chromium alloys the chromium content rangesas a rule between 15 and 25 per cent. It should be understood, however,that percentages outside these ranges may be used in. some cases.

We shall now proceed to explain'in detail the process by which the newmetal articles according to the present invention are produced. Thisprocess has been disclosed in our application for patent Ser. No.348,113, filed March 18, 1929, of which parent application Ser. No.749,922 is a continuation in part. As has been set forth in the saidapplication, we have found that nickel or nickel alloy articles farsuperior to those hitherto known are obtained by subjecting nickelpowder obtained directly by the thermal decomposition of nickelcarbonyl, to a sintering treatment by heat accompanied or followed by amechanical pressure treatment such as rolling or forging.

In determining the conditions necessary for said sintering treatment,due regard must be had to the condition of the particles of the nickelpowder to be treated. It is not only necessary that the nickel powdershould correspond to the chemical compositionindicated above, but regardmust also be had to the average size of the particles which should notexceed 10 mu and preferably range between 0.5 and 5 mu. The weight of 1liter of the powder should preferably be between 3 and 4 kilograms.

When the nickel powder contains more carbon -than indicated above, i. e.more than 0.03 per cent, it must either be subjected to a preliminaryheating together with a nickel powder which is free from carbon butcontains suflicient oxygen to combine with the carbon, or the sinteringby heat is conducted under such conditions that the carbon is removed.

The alloy metals must also be as pure as possible. The average size oftheir particles should not exceed mu in order to produce articles of asufliciently high mechanical strength.

Regard must also be had to the surface condition of the metallicparticles to be sintered. It will be readily understood that the saidparticles combine the more readily with each other, the less theirsurface is contaminated, for example with metallic oxides. Even anextremely thin superficial layer of metallic oxides may exert a greatinfluence in this respect.

The sintering by heat according to the present invention is efiected bysubjecting the metallic powder'to the action of high temperatures belowthe melting point of any constituent thereof, which treatment ispreferably carried out in an atmosphere of inert or reducing gas inorder to avoid oxidation of the metal. In this heat treatment thetemperature should be at least 300 C. and preferably ranges up to about1200 C. The time necessary for effecting sinteringdepends largely on thetemperature employed. Thus, when working at 500 C., the time requiredwill be from 1 to 8 days, and at 700- C. only from 3 to 36 hours will berequired. However, the time required for sinterlng will in any case-bemuch longer than is necessary for removing car-. bon and oxygencontained in the nickel which can be freed from said impurities byheating for example to600 C. in 15 minutes or to 700 C. in 10 minutes.The heatingfto sintering temperature is preferably conducted slowly,because the heat conductivity of the metallic powder is low and toorapid heating of the mass might therefore lead to sintering of the outerportions of the mass only while the interior does not yet sinter;thereby cracks might be formed in the mass.. Simultaneously with suchheat treatment the mass may be subjected tothe action of mechanicalpressure, for example by pressing it by means of a suitable piston. Weprefer, however, to apply a treatment by mechanical pressure, as forexample forging or rolling to the mass after it has been sintered andconsolidated by heat.

The mechanical pressure applied may be as low as 300 kilograms persquare centimeter. How-, ever, we prefer to employ higher pressures ofthe order of several thousand kilograms and, may use pressures as highas 16,000 kilograms per square centimeter or even more. 7 According toour present invention, the metallic powder can be worked up into largemetal in-- gots, which can be easily converted into articles of thedesired shape, forinstance by sawing, forging, rolling, stamping orfiling. Articles of the desired shape, such as sheets, plates, tubes,

- rods or the like can also be produced directly by subjecting thenickel powder to the sintering process by heat and pressure treatment insuitable ioulds. Theindividualparticlesofthenickel are preferably firstbrought into intimate mutual contact byshaking, tapping or ramming thepowder into the mould.

The nickel material used. for the production of the metal articles is,as already mentioned, the finely divided nickel powder prepared directlyin the form of powder from nickel carbonyl. Similarly, when anickel-iron alloy is to be produced,

the iron powder ispreferably that which is obtained directly in the formof powder from iron carbonyl.

By the addition of appropriate alloysubstances to the nickel powder themagnetic properties of the resulting metal articles can be alteredextensively; thus a material very useful for the arming and winding ofcables is obtained by mixing the nickel powder from nickel carbonyl withiron powder before it is worked up into chanical strength. The saidadvantages are mainly due to the particularly uniform size and theball-like or leaflet-like form of the particles of the nickel preparedfrom nickel carbonyl. A

. further advantage of the nickel powder prepared in this manner is thatit is non-pyrophoric and therefore is not liable to suffer ignition anddoes not cause danger to life and property in the working into nickelarticles. Owing to the aforesaid properties of the nickel powder, thearticles prepared according to the present invention have the greatadvantage of being, uniform throughout.

It should be noted that it is generally not lli very advantageous to usethe nickel alloy articles according to our present invention for coresfor electromagnets or the like, especially such as are operated withhigh frequency currents, without' suitably subdividing them byarrangement in plates or the like, because they may give rise toconsiderable eddy current losses due to their being free from insulatinginclusions, such as oxidic layers on the particles of the nickel powder.Thefollowing examples will further illustrate the nature of theinvention but the invention is not restricted to these examples. Theparts are by weight.

Example 1 A mixture of nickel carbonyl and iron carbonyl containingnickel and iron in equal amounts by weight is evaporated and decomposedat 260 C. in the free space of a heated vessel. A metal powder isobtained which contains 48.8 per cent of nickel, 48.8 per cent of iron,1.2 per cent of carbon and 1.2 per cent of oxygen..

A portion of this powder is moistened with water and dried at 150 C. Itthen contains 47.9 per cent of nickel, 47.9 per cent of .iron, 1.2 percent of carbon and 3 per cent of oxygen.

100 kilograms of the powder initially obtained are mixed with 80kilograms of the powder en- 'riched in oxygen. The mixture is filledinto a mould made of refractory material and heated for 4 hours at 1200C. while excluding air. The sintered block is forged into bars which arerolled, while warm, into bands of 5 millimeters thickness. The bands arerolled in the cold to a thickness of 1.2 millimeters, heated for 2 hoursat 900 C. in an atmosphere of hydrogen, and further rolled in the coldto a thickness of 0.35 millimeter. They are then made into coils andheated for 3 hours at 1000 C. in an atmosphere of hydrogen. -Theresulting material possesses an initial permeability of'5000, a maximumpermeability of 65000 and a coercive power of 0.03

bands. Gauss.

Example 3 99.5 kilograms of nickel powder obtained from nickel carbonyland containing 0.03 per cent of carbon are mixed with 0.5 kilogram ofman ganese powder and heated for 10 hours at 1200 C. in an atmosphere ofdry hydrogen. The material is rolled into bars while hot and thenquenched in cold water. The extensibility of the resulting material isat least 10 per cent higher than that of the material hitherto availablein commerce which has substantially the same composition.

Example 4 60 parts of nickel powder obtained from nickel carbonyl aremixed with 40 parts of copper powder obtained,by'precipitation by means"of zinc dust from a copper sulphate solution. The mixture is heated for8 hours at1000 C. in a current of hydrogen. The sintered block which percent greater than that of commercial Monel than 0.002 per cent ofsulphur and having an average size of the particles not exceeding 10 mu,and of at least one further metal from the group consisting of iron,chromium, copper and manganese, said further metal having an averagesize of the particles not exceeding mu, said heating operation resultingin consolidation of the mixture of metal powders into a nickel alloyarticle, said consolidation being assisted by the application ofmechanical pressure at a time following the beginning of the heating.

2. The process of producing nickel-iron alloy articles containing notmore than 0.3 per cent of carbon which comprises heating to a sinteringtemperature a nickel-iron powder obtained directly by the thermaldecomposition of a mix-.

ture of nickel carbonyl and iron carbonyl, said powder being free frommanganese, magnesium, copper, silicon and phosphorus, containing notmore than 0.002 per cent of sulphur and having an average size of theparticles not exceeding 10 mu, said heating operation resulting inconsolidation of the powder into a nickel-iron alloy article, saidconsolidation being assisted by the application of mechanical pressureat a time following the beginning of the heating.

3. The process of producing nickel alloy articles containing not morethan 0.3 per cent of carbon which comprises heating to a sinteringtemperature a mixture composed of a nickel powder obtained directly bythe, thermal decomposition of nickel carbonyl, said nickel powder beingfree from manganese, magnesium, copper, silicon and phosphorus andcontaining not more than 0.002 per cent of sulphur and having an averagesize of the particles not exceeding 10 mu, and of a substantial amountof at least one further metal from the group consisting of iron,chromium, copper and manganese, said further metal having an averagesize of the particles not exceeding 100 mu, said heating operationresulting in consolidation of the mixture of metal powders into a nickelalloy article, said consolidation being completed by rolling thesintered material to obtain a solid body.

4. The process of producing nickel articles containing not more than 0.3per cent of carbon which comprises heating to a sintering temperature amixture composed of a nickel alloy powder obtained directly by thethermal decomposition of nickel carbonyl, said nickel powder being freefrom manganese, magnesium, copper, silicon and phosphorus and containingnot more than 0.002 per cent of sulphur and having an average size ofthe particles not exceeding 10 mu, and of a substantial amount of atleast one further metal from the group consisting of iron, chromium,copper and manganese, said further metal having an average size of theparticles not exceeding 100 mu, said heating operation resulting inconsolidation of the mixture of metal powders into a nickel alloyarticle, said consolidation being completed by rolling the sinteredmaterial to obtain a solid and compact body.

5. Nickel alloy articles obtained by a process as claimed in claim 1,containing nickel and at least one of the metals iron, chromium, copperand manganese, less than 0.002 per cent of sulphur and less than 0.3 percent of carbon, and capable of being rolled in the cold.

' LEO SCHLECHT.

WALTER SCHUBARDT.

